Their modus operandi is invariably the same: pay-as-you-go mobile, un-registered and usually destroyed within a week of purchase or immediately after the crime.
Despite all these apparent benefits however, the modern day criminal is still faced with a number of problems; they either telephone friends and family, associates and fellow criminals to tell them the mobile phone number for this week or the near future or they get around this by carrying a ‘clean’ mobile phone that is solely used for friends and family, keeping criminal activity to the disposable ‘dirty’ mobile phone.
Increasingly, reliance is made by the Prosecution on telephone evidence and the focus, when the handset has gone missing, is typically on “attribution” which is the process of working out who was using a particular mobile phone and therefore who made and received the calls in the records held by the service provider.
What is cell site analysis?
Closely related to the process of attribution is the branch of forensic telecommunications that deals with geographic positioning analysis. This is commonly called cell site analysis due to the basic data being derived from the position of the mobile phone mast (cell site) that handled a call or a series of calls.
Can cell site pinpoint exact location?
Cell Site Analysis can't pinpoint the exact location of a mobile phone but through careful measurement of cell site coverage and analysis of other adjacent cells, opinions can be formed on the whereabouts of a person operating a mobile phone.
The prosecution will often review call data records to establish common numbers and the friends and family calls from a clean phone and then using cell site analysis of this clean phone they will attempt to establish if the dirty phone was in the same geographic location.
How accurate is it?
We are starting to see prosecution reports that suggest that because two phones are cell sited in the same geographic location that it is “likely” that they are in the hands of the same individual. These suggestions are worrying. Cell site analysis is not an exact science and is only completely reliable when used to establish where a person was not located rather than where they were located.
How far away can a cell site be?
In theory a mobile phone can be up to 35 kilometres from the serving cell. In reality, the cell site normally selected to handle a call will be much closer than this theoretical maximum and in major cities is usually likely to be no more than a few hundred meters away. In suburban districts, 4-5 kilometres is more likely. But these broad rules cannot be relied on in all circumstances and any meaningful location derived simply by conducting a desk-based exercise from the call data records.
What is the recommended procedure for cell site analysis?
As part of the preparation of the defence case, we at IT Group always recommend an onsite measurement of the cell sites with the correct instruments and trained engineers. This establishes whether a particular cell has a directional antenna, is limited in range or possibly has an unusually high range. Specific tests establish whether or not it is possible to make or receive a call at a particular location and to be served by the cell site being analysed.
We present our reports in plain English with a heavy reliance on maps that we generate individually to set out in clear terms where a mobile phone could have been and more importantly where it could not. With practically every case we are instructed in we identify anomalies in cell site ranges and in the analysis undertaken by the prosecution. On occasions we have confirmed an alibi that may initially have been discounted by the prosecution.